Computer technology has advanced to the point where a dental prosthesis may be milled from a solid block of material based on three-dimensional digital data corresponding to a proposed shape of the dental prosthesis. The dentist first makes an impression of a patient's existing dentition. Typically, this includes nearby surfaces where the prosthesis is to be located in the patient's mouth. This is accomplished by the dentist first drilling away any unwanted dental tooth structure and then having the patient bite into an impression material that forms a negative impression of the patient's dentition, including the tooth structure to which the dental prosthesis is to be attached. This negative impression is then filled with dental die stone to make a model of the tooth structure to which the dental prosthesis is to be attached and adjacent teeth, particularly the teeth immediately above and to the sides of the tooth structure to which the dental prosthesis is to be attached. This model of the patient's dentition captures an impression of the occlusion surfaces between upper and lower aligned teeth and the configuration of the tooth structure to which the dental prosthesis is to be attached.
The computer aided design equipment used to make a dental prosthesis has an scanner that is used to scan the surfaces of the model. Scanning may be accomplished either with optical techniques using laser or non-laser light or tactile techniques where a probe physically contacts the tooth's surface. The computer aided design equipment converts the model's surfaces into three-dimensional digital data corresponding to the physical shape of the model. This original data collected during scanning is then used to create an image of the proposed shape for the prosthesis on a screen of a computer monitor. The computer aided design equipment is programmed to allow the user, with the aid of a mouse and employing conventional point and click techniques, to change the shape of the image. The original image displayed on the monitor screen needs to be adjusted to modify the original image to correspond to the ultimate shape of the dental prosthesis.
Because the data originally collected during scanning isn't precise enough to make the dental prosthesis directly based on this data, the user can and does make adjustments to the data originally provided by the scanner so that the dental prosthesis, at least in theory, fits properly into the patient's mouth. After making such adjustments to the data collected by the scanner, the adjusted three-dimensional digital data is then forwarded to an automatic milling machine which then mills away the unwanted material from a block to form the dental prosthesis. Typically, the block of material is a ceramic, titanium, or composite plastic material. One of the perceived advantages of this technique is the elimination of conventional investment casting of a wax pattern of the dental prosthesis, which has conventionally been used to make a dental prosthesis.
Although this computer aided design equipment proposes to eliminate conventional investment casting, it suffers from a number of drawbacks that prevent greater utilization of this technology. First, it is impractical to make dental prosthesis from such precious metals as gold and platinum using this technology because so much of the precious metal is lost during the milling process. Second, the adjustments made to the image based on the original data collected during scanning usually fail to create a dental prosthesis that properly fits into the patient's mouth. The inaccuracies in the shape of the dental prosthesis so produced using this technology are particularly acute along the marginal edges of the prosthesis adjacent the margins where the treated (drilled) tooth surfaces of an individual tooth are contiguous with the untreated (undrilled) tooth surfaces of this individual tooth.